1. Field of the Invention
This invention relates to a method of controlling a stepping motor and more particularly to a method for rapidly, accurately and effectually driving a rotor of a stepping motor in response to the position of the rotor.
2. Description of the Prior Art
In stepping motors of the type with which this invention is concerned, the motor generally consists of a rotor adapted for connection to a mechanical load and a stator having a number of phase windings. As an example, consider a printer wherein one stepping motor can be used to perform vertical indexing of a paper line feed and another stepping motor can be used for rotation of a disc-shaped print wheel. A suitable electrical drive logic or control unit operates to selectively energize the windings in such a manner as to create an internal magnetic field which produces a torque that urges the rotor to assume a mechanical position in line with the resultant magnetic field. The drive logic supplies the motor with advance pulse signals and changes the energization of the windings in a sequential step-by-step fashion, to cause the magnetic field to move in a similar step-by-step fashion.
In general, two methods are known for driving stepping motors. One method involves supplying advance pulse signals to only one phase winding at a time. The other method involves supplying advance pulse signals to selected two or more phase windings simultaneously. In the first method, there is produced less torque for operating the rotor, than in the second method. Thus, using the first method, it is difficult to rapidly accelerate and decelerate rotation of the rotor in the process of driving the rotor to a desired position in a short period of time. In the second method, the rotor is strongly rotated. However, disadvantageously, in the second method, electric power is dissipated as unrequired heat, more so than is the case using the first method.